與str_extract [R

多consitions我有一個數據幀如下與str_extract [R

1  Tertiary seen. 
    2  No tertiary seen. 
    3  No anything seen. 
    4  Tertiary everywhere.

我想補充，只有當三級看到一列，但不是在正則表達式沒有。* \。被看到。

1  Tertiary seen.  Tertiary 
    2  No tertiary seen.  NA 
    3  No anything seen.  NA 
    4  Tertiary everywhere. Tertiary

我知道我可以使用str_extract |但&似乎並沒有被接受如下

Mydata$newcol<-str_extract(Mydata$Text,"[Tt]ertiary&!No.*[Tt]ertiary\\.")

來源

2016-12-04 Sebastian Zeki

我會用'MYDATA $ NEWCOL去[grepl（「（否）三級？！」，MYDATA $文本，perl的= TRUE）] < - 「三級」'（負向後看） –

啊哈。負面的後顧之憂。謝謝。請作爲答覆發佈 –

你可以嘗試一個Negative lookebehind，像

Mydata$newcol[grepl("(?!No)Tertiary", Mydata$Text, perl = TRUE)] <- "Tertiary"

來源

2016-12-04 11:08:34

「AND」模式可以用「NOT（NOT A NOT NOT B）」模式表示。另見regex - Regular Expressions: Is there an AND operator? - Stack Overflow。

library(dplyr) 
library(stringr) 

Mydata <- data_frame(
    Text = c("Tertiary seen.", 
      "No tertiary seen.", 
      "No anything seen.", 
      "Tertiary everywhere.") 
) 

Mydata %>% 
    mutate(
    newcol = str_extract(Text, "^(^[Tt]ertiary|^No.*[Tt]ertiary\\.)") 
) 
# A tibble: 4 × 2 
# Text newcol 
# <chr> <chr> 
# 1  Tertiary seen. Tertiary 
# 2 No tertiary seen.  <NA> 
# 3 No anything seen.  <NA> 
# 4 Tertiary everywhere. Tertiary

來源

2016-12-04 12:04:34 Keiku

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